The present invention relates to an optical amplifier, a method of controlling, an excitation light source in an optical amplifier, and a method of controlling an optical amplifier which are suitably employed for use in, for example, a wavelength multiplexing optical communication system, when increasing or decreasing the number of channels in signal light (the number of wavelengths to be multiplexed in signal light) while the system is in operation.
In the recent years, wavelength multiplexing optical communication systems have been investigated and developed very actively, and studies have taken place to develop a system which is capable of increasing the number of channels in signal light in answer to the demand for communications.
In addition, a desire exists to upgrade the amplification scale of an optical amplifier, being an essential component of this wavelength multiplexing optical communication system, in accordance with the increase in the number of channels. A similar need also exists on an optical amplifier included in a light wave network or the like.
To meet such a requirement, consideration may be given to a construction in which an optical amplifier capable of amplifying multi-wavelength (for example, approximately 32 channels) multiplexed signal light is introduced from the initial operation into an optical communication system, thus coping with the increase in the number of channels.
In this instance, although being equipped with an excitation light source, for handling the multi-wavelength multiplexed signal light, the optical amplifier is required to be provided with an excitation light source which is capable of supplying a large quantity of excitation light.
However, in addition to the fact that the excitation light source is usually expensive, a small number of channels (for example, approximately 4 channels) are frequently used at the beginning of the system operation, and therefore, if such an optical amplifier capable of dealing with multi-wavelength multiplexed signal light is employed from the first system operation, there is a problem in that the initial investment for the equipment increases to lower the investment efficiency.
For this reason, in order to enhance the equipment investment efficiency, consideration can be given to that another excitation light source is added to the existing optical amplifier in accordance with an increase in the number of channels in signal light while the optical communication system is in operation.
However, if the additional excitation light source is introduced into the control loop of the preexisting excitation light source, the control of these excitation light sources can frequently go unstable. More specifically, supposing that the quantity of an excitation light required for when the optical amplifier obtains a predetermined gain (excitation optical power) is P, difficulty is encountered to singly determine the combination of excitation optical powers of these two excitation light sources to be P in total, so that a plurality of stable operating points appear, which results in unstable excitation light source control.
On the other hand, consideration should also be given to the fact that, after an additional excitation light source is installed to increase the number of channels in signal light, the number of channels is decreased depending on the demand for communications while the optical communication system is in operation, and further, that a need can occur to remove the additionally installed excitation light source.
Accordingly, in the optical communication system being in operation, in order to coping with the increase/decrease in the number of channels, there is a need to provide a construction which allows the installation or the removal of an additional excitation light source without interfering with the working channels.
The present invention has been developed in consideration of such problems, and it is therefore an object of this invention to provide an optical amplifier, an excitation light source control method for use in an optical amplifier and an optical amplifier control method which are capable of stably installing or removing an additional excitation light source in accordance with an increase/decrease in the number of channels in signal light even if the optical communication system is in operation.
For this purpose, an optical amplifier according to this invention comprises an optical amplifying section for amplifying and outputting inputted signal light, a plurality of excitation light sources each for supplying excitation light to the optical amplifying section and an excitation light source control section for controlling operations of the excitation light sources, wherein the excitation light sources are composed of a main excitation light source, whose output amount of the excitation light to be supplied to the optical amplifying section is to be controlled by the excitation light source control section, and an auxiliary excitation light source, whose output of excitation light to be supplied to the optical amplifying section is to be turned on/off under control by the excitation light source control section in accordance with an increase/decrease in the number of channels in signal light to be inputted to the optical amplifying section, and the excitation light source control section includes a control section, which executes control so that the main excitation light source supplies excitation light to the optical amplifying section when the number of channels in signal light to be inputted to the optical amplifying section is equal to or less than a predetermined number of channels, and the main excitation light source and the auxiliary excitation light source cooperatively supply excitation light to the optical amplifying section when the number of channels in the signal light is more than the predetermined number of channels.
Furthermore, an optical amplifier according to this invention comprises an optical amplifying section for amplifying and outputting inputted signal light, a plurality of excitation light sources each for supplying excitation light to the optical amplifying section and an excitation light source control section for controlling operations of the excitation light sources, wherein the excitation light sources are composed of main and auxiliary excitation light sources in which output amounts of the excitation light to be supplied to the optical amplifying section are to be controlled by the excitation light source control section, and the excitation light source control section includes a control section, which executes control so that the main excitation light source supplies excitation light to the optical amplifying section when the number of channels in signal light to be inputted to the optical amplifying section is equal to or less than a predetermined number of channels, and the main excitation light source and the auxiliary excitation light source cooperatively supply excitation light to the optical amplifying section when the number of channels in the signal light is more than the predetermined number of channels.
On the other hand, according to this invention, there is provided an excitation light source control method for use in an optical amplifier which comprises an optical amplifying section for amplifying and outputting inputted signal light, a plurality of excitation light sources each for supplying excitation light to the optical amplifying section and an excitation light source control section for controlling operations of the excitation light sources, with the excitation light sources being composed of a main excitation light source, made so that the output amount of the excitation light to be supplied to the optical amplifying section is to be controlled by the excitation light source control section and an auxiliary excitation light source, whose output of excitation light to be supplied to the optical amplifying section is to be turned on/off under control by the excitation light source control section, in a state where the main excitation light source supplies the excitation light the amount of which corresponds to the number of channels in signal light to be inputted to the optical amplifying section, when the number of channels in signal light to be inputted to the optical amplifying section is more than a predetermined number of channels, the main excitation light source is controlled to output excitation light in a quantity corresponding to the number of channels in the signal light and the auxiliary excitation light source is subsequently controlled to output the excitation light so that a quantity of the excitation light outputted from the auxiliary excitation light source increases, and the total amount of excitation light outputted from the main excitation light source and the auxiliary excitation light source corresponds to the number of channels.
Moreover, according to this invention, there is provided an excitation light source control method according to this invention for use in an optical amplifier which comprises an optical amplifying section for amplifying and outputting inputted signal light, a plurality of excitation light sources each for supplying excitation light to the optical amplifying section and an excitation light source control section for controlling operations of the excitation light sources, with the excitation light sources being composed of main and auxiliary excitation light sources in which the output quantities of their excitation light to be supplied to the optical amplifying section are controlled by the excitation light source control section, in a state where the main excitation light source supplies the excitation light whose quantity corresponds to the number of channels in signal light to be inputted to the optical amplifying section, when the number of channels in signal light to be inputted to the optical amplifying section is more than a predetermined number of channels, the main excitation light source is controlled to output the excitation light in a quantity corresponding to the number of channels in the signal light and the auxiliary excitation light source is subsequently controlled to output the excitation light, and further, the total amount of excitation light outputted from the main excitation light source and the auxiliary excitation light source are controlled to correspond to the number of channels.
Furthermore, according to this invention, there is provided an excitation light source control method for use in an optical amplifier which comprises an optical amplifying section for amplifying and outputting inputted signal light, a plurality of excitation light sources each for supplying excitation light to the optical amplifying section and an excitation light source control section for controlling operations of the excitation light sources, with the excitation light sources being composed of a main excitation light source, whose output quantity of the excitation light to be supplied to the optical amplifying section is to be controlled by the excitation light source control section and an auxiliary excitation light source, whose output of excitation light to be supplied to the optical amplifying section is to be turned on/off under control by the excitation light source control section, in a state where the main excitation light source and the auxiliary excitation light source cooperatively supply the excitation light whose quantity corresponds to the number of channels in signal light to be inputted to the optical amplifying section, when the number of channels in signal light to be inputted to the optical amplifying section is equal to or less than a predetermined number of channels, the output of excitation light from the auxiliary excitation light source is stopped, and subsequently, the main excitation light source is controlled to output the excitation light whose quantity corresponds to the number of channels in the signal light after decreased.
Still further, according to this invention, there is provided an excitation light source control method for use in an optical amplifier which comprises an optical amplifying section for amplifying and outputting inputted signal light, a plurality of excitation light sources each for supplying excitation light to the optical amplifying section and an excitation light source control section for controlling operations of the excitation light sources, with the excitation light sources being composed of main and auxiliary excitation light sources, in which the output amounts of their excitation light to be supplied to the optical amplifying section are to be controlled by the excitation light source control section, in a state where the main excitation light source and the auxiliary excitation light source cooperatively output excitation light in a quantity corresponding to the number of channels in signal light inputted to the optical amplifying section, when the number of channels in signal light inputted to the optical amplifying section becomes equal to or less than a predetermined number of channels, the output of excitation light from the auxiliary excitation light source is stopped and the main excitation light source is subsequently controlled to output excitation light in a quantity corresponding to the number of channels in the signal light after decreased.
An optical amplifier according to this invention includes an amplification optical fiber, wherein the amplification optical fiber is doped with a rare earth element and receives a plurality of optical signals different in wavelength from each other, with the optical amplifier being designed so that an increase/decrease in the number of excitation light sources, which supply excitation light thereto, are allowed in accordance with the number of optical signals to be inputted.
Moreover, a method of controlling an optical amplifier according to this invention comprises identifying a number of optical signals having different wavelengths, and varying the number of excitation light sources, which supply excitation light to an amplification optical fiber receiving a plurality of optical signals, in accordance with the number of optical signals.
Thus, according to this invention, there is an advantage in that, even in the case that the output of excitation light from the auxiliary light source is controlled in connection with the increase/decrease in the number of channels in inputted signal light, excitation light can be supplied to the optical amplifying section in a quantity corresponding to the number of channels increased or decreased without adversely affecting the channels being in operation. Accordingly, even if the optical communication system is in operation, it is possible to stably install or remove the auxiliary excitation light source in accordance with the increase/decrease in the number of channels in signal light.